Micropaleontology
is the study of microscopic fossils. It is the largest
discipline in paleontology, just as microfossils are by
far the most abundant of all fossils. Although nearly
invisible, micro-organisms at the base of the food chain
make up nearly 90 per cent of the biomass in oceans and
lakes. The variety of life forms at this level is almost
incomprehensible, and while only a few kinds leave solid
remains that fossilize, even these few can be so abundant
that in places they form mountains of pure fossil remains.
The limestone of the plateau from which the Sphinx and
Pyramids are carved is actually a mass of foraminifera
(left, in a microscopic view), preserved in a vast
offshore formation that, 40 million years ago, extended
from France to Burma. The Chalk Cliffs of Dover, another
microfossil marvel, is a layer hundreds of feet thick
all across western Europe that consists of nothing but
sub-microscopic coccoliths (see below). In other
parts of the world, solidly packed remains of diatoms
(see below) make up formations of thin-layered
diatomite hundreds of feet thick that are quarried for
industrial uses.

The
abyssal floor of the ocean, which occupies more than half
of the earth's surface, is buried under a carpet of microfossils
that slowly piles up like layers of dust over the millenia.
Changes in the abundance and types of microfossils from
year to year, over millions of years of undisturbed accumulation,
makes an exquisitely detailed record of climate change,
plate tectonics, and biological evolution. Each time a
new species of free-floating marine micro-organism (such
as the dinoflagellate, right) evolves, it quickly
spreads throughout the oceans in countless billions, forming
a worldwide marker in the fossil record. Such marker horizons
allow geological events in different parts of the world
to be related in a global earth history. For instance,it
was the microfossil "tape recorder" that proved
that reversals of the polarity of the earth's magnetism
were worldwide events. Microfossil data also revealed
that changes in sea levels, temperature, and glacial advances
were synchronous worldwide, proving the reality of global
climate changes more accurately than geochemical dating
methods.Recently, micropaleontology has shown how oscillations
in the earth's orbit and tilt lead to cycles in global
climate, including the Ice Ages.

Microfossils
are vital to oil exploration. Because of their tiny size
and great abundance, they occur unbroken in the rock fragments
brought up by drilling into the deeply buried ocean formations
and lake beds where oil is found. By comparing the characteristic
fossils from each formation as they are penetrated by
the exploratory drills, geologists can unravel the geometry
of the strata far beneath the surface and locate the domes
and traps that may hold oil. The condition of the fossils,
as well, indicates whether the petroleum source rocks
have been buried and heated sufficiently to generate oil
from trapped organic matter. Most importantly of all,
the organic matter itself is almost entirely from ancient
micro-organisms that make up the ocean's biomass. (Diatoms,
as at left, are important trace fossils as well as the
primary source of oil.)

Most
of the principal microfossil groups are Protista. These
are single-celled or colonial Eukaryotes (i.e. organisms
with cell nuclei and chromosomes), that are more advanced
than Prokaryotes (archaea and bacteria), while being ancestral
to higher eukaryotes such as fungus, plants and animals.
The foraminifera and radiolaria are two
orders of predatory (i.e., non-vegetative) protists, related
to amoeba in the Sarcodina, that secrete multi-chambered
limy and siliceous shells, respectively.

Vegetative
(photosynthesizing) protists with fossilizing hard parts
include coccoliths, with complex structures (as
in the coccolith at the right, and on our splash panel
) that break down into submicroscopic but readily
identifiable limy disks and stars, and the diatoms,
with single-chambered circular or ovoid valves of silica
that fit together like pillboxes. The dinoflagellates
and their extinct relatives acritarchs, with
whip-like propulsive flagella and chitinous body casing,
are both predatory and photosynthesizing; they are represented
in the fossil record by the cysts that they make during
one part of their life cycle.

Important groups of microfossils are also found among
animals and plants, for instance the ostracodes,
tiny free-swimming crustaceans in the same family as
barnacles. Spores and pollen from fungi and plants
give important paleonvironmental data. In ancient strata
conodonts, the teeth of an extinct group of soft-bodied
invertebrates, are important stratigraphical guides,
and icthyoliths, or fish teeth, are used for
deep-sea dating.

Recommended
reading covers the biology of microfossils and their role in unravelling
the history of life and the great geological events that
shaped the modern oceans and continents.